Conventionally, there is known a projection-type image display device that projects incoherent light that is emitted from a light such as a halogen lamp or a high-pressure mercury lamp onto a planar image display element such as a liquid-crystal light bulb, and enlarges and projects the emitted light from that image display element by a projection lens on a projection plane to display the image.
In this type of projection-type image display device, since incoherent light is used, there has been the problem of electricity consumption being great, and the problem of the brightness of the display image being low. Also, since the wavelength bandwidth of the incoherent light that is emitted from the light source is wide, it has been difficult to broaden the chromaticity range. Moreover, since a planar image display element is used as the image display element, reducing the size of the device has been difficult. Also, when a display image is not projected within the focal depth of the projection lens, the display image is not in focus. For that reason, there is a need for the user to adjust the focus in accordance with the position of the projection plane, and so there has been the problem of impairing convenience.
As a technique for solving the aforementioned problems, an image display device that uses a laser light source that emits laser light has been proposed or developed. Among such kinds of image display devices, there is a scanning-type image display device that displays an image by projecting laser light that is emitted from a light source onto a projection plane by two-dimensional scanning (horizontal scanning and vertical scanning) with a scanning unit.
In the aforementioned scanning-type image display device, in order to project a large screen in a short projection distance, a scanning unit with a large scan angle is necessary. As the scanning unit, it is possible to use a resonance-type micromechanical mirror or galvano scanner or the like. In this case, when the scan angle is increased, the driving current of the electrostatic actuator or electromagnetic actuator for driving increases, leading to the problem of power consumption becoming large. Also, when the scan angle of the resonance-type micromechanical mirror increases, the durability of the device falls, and there is the risk of the hinge member that rotatably supports the mirror breaking For this reason, obtaining reliability has been a problem.
As technology that solves the aforementioned problems and increases the scan angle of the scanning unit, for example there is the scanning device disclosed in Patent Document 1. FIG. 14 is a diagram for describing the scanning device described in Patent Document 1.
In the scanning device shown in FIG. 14, a scanning unit 131, a condensing lens G1 and a diverging lens G2 are arranged from the light source not shown to the emission side. These are arranged so that the focal position f1 of the emission side of the condensing lens G1 and the focal position f2 of the incident side of the diverging lens G2 agree. According to this constitution, the exit angle θ2 of laser light that is emitted from the diverging lens G2 can be made greater than the entry angle θ1 of the laser light that is incident on the condensing lens G1 from the scanning unit 131. As a result, it is possible to obtain a large scanning range on the projection plane (not shown).
Among such scanning-type image display devices, there is a constitution that has a beam waist arranged on the projection plane in order to broaden the range of adjusting the focus, and to display a high-definition image (for example, refer to Patent Document 2).